[time-nuts] Re: Ublox M6T -M8T

[Hal Murray]

Matthias Welwarsky said:
> Only frequencies that are even multiples of the internal crystal frequency
> (48MHz) are "clean". Everything else is, as Bob puts it, "drop a pulse, add a
>  pulse" approximations. However, that's normally easy to filter. 

How clean?  It's a GPS, not a GPSDO, so I'd expect the 48 MHz is free running 
rather than locked to GPS time.

Take the PPS case.  There will be adds/drops going on to correct for the 
frequency error in the 48 MHz crystal.  The pattern will change as the 
frequency changes with temperature or whatever.  That's how you get hanging 
bridges.  :)

Assume it is off by roughly 1 PPM.  That's well within specs for a crystal.  I 
just want a number for the back of an envelope.

For 10KHz, 1 PPM is an add/drop every 100 cycles.  I'll bet you can catch that 
on a scope running in persistance mode.



-- 
These are my opinions.  I hate spam.